Numerical control systems are equipped with a numerical controller (CNC) and a man-machine interface controller (MMC)M which interactively performs data input/output operations and processes the data. The man-machine interface controller has some peripherals such as input devices (e.g., keyboard and mouse) and a display device (e.g., CRT or liquid crystal display) for this interactive operations.
In many cases, the numerical controller and man-machine interface controller are installed in a common cabinet and connected with each other by a parallel bus. Thanks to this parallel bus connection, a high-speed data transfer is provided between the numerical controller and man-machine interface controller. However, it is impossible to locate the man-machine interface controller at a distance from the numerical controller because of difficulty in extending the parallel bus. If there was no such a restriction with the location of the man-machine interface controller, it would be possible to place the man-machine interface controller anywhere the machine operator would feel convenient for efficiency of his/her work. For this reason, there has been a demand that the man-machine interface controller and the numerical controller be connected by a long transmission line.
One traditional solution for the above demand is a system that interconnects the buses of the two controllers via an RS-232-C line, which is one of the data communications methods standardized by the Electronic Industry Association (EIA) in the United States of America. According to this system configuration, the man-machine interface controller can be located tens of meters away from the numerical controller, and both processors can exchange data using a predetermined software protocol.
For example, when the man-machine interface controller is about to make access to some memory data in the numerical controller, the man-machine interface controller first outputs a data transfer request to the numerical controller via the RS-232-C interface. Upon reception of the data transfer request, the numerical controller parses the request and sends the requested data in its memory back to the man-machine interface controller, thereby allowing the man-machine interface controller to get its desired data.
The above-described connection by the RS-232-C interface, however, always takes two steps when the man-machine interface controller tries to read memory data in the numerical controller. First, the man-machine interface controller issues a data transfer request, and second, the processor in the numerical controller must support actual data transfer operations. In other words, the man-machine interface controller cannot directly access the memory within the numerical controller. As a result, the man-machine interface controller in need of some data in the numerical controller, must wait for the numerical controller sending the data, thus spending significant time to obtain the data. Also, the processor in the numerical controller must take care of the data transfer for the man-machine interface controller in addition to its regular duty, namely, numerical control. This extra burden of the processor could degrade its processing performance in various areas.
As described above, when the man-machine interface controller and the numerical controller are set apart from each other, the conventional numerical control system slows down in its data processing operations. This is due to a lack of direct access capability from the man-machine interface controller to the numerical controller's memory.